Launch SFR by force-enabling the feature flag in the plugin

[techanvil]

Feature Description

In order to launch Setup Flow Refresh, we need to override the setupFlowRefresh feature flag status to true in the plugin. We can use the googlesitekit_is_feature_enabled filter to achieve this.

We're unable to progressively roll out the feature because we can't enable the flag via the service for new users who haven't yet signed in.

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Acceptance criteria

• The setupFlowRefresh feature flag is overridden to true in the plugin.
• The Setup Flow Refresh feature is enabled by default and continues to work as expected.

Implementation Brief

• In includes/Plugin.php:
  • Add a plugin-level googlesitekit_is_feature_enabled filter callback that forces setupFlowRefresh to true.
  • Keep the callback scoped to setupFlowRefresh only; return the incoming $feature_enabled value unchanged for every other feature.
  • Register the callback with higher priority than the remote-features activation callback so the forced value is authoritative.
  • Keep the override active for all users (including signed-out/new users) so SFR is enabled by default without remote-feature dependency.

Test Coverage

• Add/extend PHPUnit coverage in tests/phpunit/integration/PluginTest.php with respect to the above changes.
  • Assert apply_filters( 'googlesitekit_is_feature_enabled', false, 'setupFlowRefresh' ) returns true after plugin registration.
  • Assert non-target flags still follow normal behavior.
• Fix any failing tests.

QA Brief

Changelog entry